Cities and towns throughout the world depend on clean potable water supplies. The dependence on clean water has increased as the population of the world has increased, especially as industrial use of rivers and lakes have become commonplace. The increased industrial use of fresh water supplies has resulted in a corresponding decrease in water quality throughout the world, due principally to industrial related release of pollutants into the water supplies. The decrease in water quality is contravening to the world's increased dependence on clean potable water supplies, requiring a concerted effort toward both minimizing the release of pollution into the water supplies and removing existing pollution in water supplies throughout the world.
One particularly concerning pollutant in many water supplies is hexa-valent chromium. Hexa-valent chromium is a valence of chromium, a metallic element of atomic number 24, group VIB of the periotic table, whose ions can form many different coordinated compounds in aqueous solution. Hexa-valent chromium has been used in numerous industrial applications, for example, as an alloying and plating element on metals and plastic substrates, as a protective coating within the automobile industry, as a biocide in cooling waters, and as a constituent of inorganic pigments. Due to its widespread use in numerous manufacturing processes in numerous geographic locations, over a longer period of time, six-valent chromium and chromium containing compounds, have found their way into many of the water supplies of the world. This especially true for ground water supplies in and around locations that participated in the above described industrial applications.
Hexa-valent chromium has been shown to be carcinogenic, i.e., a cause of cancer, and corrosive to tissue, i.e., causing ulcers and dermatitis over prolonged contact with the skin. High or even moderate levels of hexa-valent chromium in a water supply is therefore a major health concern for those individuals consuming or coming in contact with such water supply. Therefore, there is a need to find efficient, cost effective hexa-valent-chromium removal systems for use on water sources through the world.
Conventional methods for removing hexa-valent chromium (Cr+6) from water supplies have focused on either anion exchange resins or chromium reduction and precipitation techniques. In particular, where the Cr+6 is at very low concentrations, an ion exchange resin is utilized for its removal. However, where the Cr+6 is at higher concentrations, the Cr+6 is first reduced to Cr+3 and precipitated out of solution as chromium hydroxide (Cr(OH)3) (requiring the use of sulfur dioxide, sodium sulfate, sodium metabisulfite, and zero-valent iron). Note that chromium hydroxide has very low solubility between pH 5 and 10, i.e., the range of pH for most water supplies. These commercial techniques for removal of Cr+6 from water supplies therefore require either the use of expensive ion exchange resins or reduction to form a precipitate of the Cr+3 from the water source.
Against this backdrop the present invention was developed.